The invention relates to a low pressure chill casting method for casting metal castings such as cylinder heads or engine blocks of combustion engines or the like, which cast components have walls which are considerably thinner in some regions than in their remaining regions, in which method by means of gas pressure liquid metal is forced from a melt container through a riser tube into a mold.
While in known gravity chill casting methods during charging metal is allowed to fall over the entire mold height, whereby strong turbulence occurs in the mold with the known disadvantageous consequences for the metal structure, in known low pressure chill casting methods by introducing the metal into the mold from beneath and allowing it to rise in the mold quieter metal flow is achieved, the molding speed being adaptable at each phase to the desired mold filling. According to previously generally accepted teaching, in known low pressure casting methods the casting molds are so arranged that the thickest wall parts of the cast component lie in the vicinity of the gating, while the thin walled regions lie spaced therefrom. This takes place with a view to enabling feeding of the cast component during its solidification exclusively by melt subsequently pressed from the riser tube, i.e. the solidification should begin in the regions of the cast component remote from the gating and propagate to the gating (see handbook "Kckillen fur Leichtmetallguss" by Professor Philipp Schneider, Giesserei-Verlag 1986, pages 205 and 206). Since in such a situation for the mold the predominantly thick walled regions of the cast components in the vicinity of the gating solidify relatively slowly in the mold, the formation of coarse crystalline structure with precipitation of coarse inter-metallic compounds in this region of the casting is the result. This has however proved to be very unsatisfactory with cast components which in use are subject to high loading in the region of their predominently thicker wall portions, as is for example the case in cylinder heads in the combustion region. A further disadvantage of these known methods of operation arises in that to achieve trouble free mold filling into the thin wall regions it is necessary to work with correspondingly increased casting temperatures which in turn must act disadvantageously on the overall solidification time, i.e. the duration of a casting cycle and also on the casting quality.